1. Field of the Invention
The present invention relates to the field of three-dimensional imaging. More specifically, the present invention relates to a method and to a system for the reconstruction of ultrasound image data using an angular scanning technique producing a plurality of planes spaced around an axis of rotation of a scanning means used to acquire the image data.
2. Description of the Prior Art
Three-dimensional (3D) ultrasound imaging is a technique in which a set of spatially related two dimensional ultrasound slices (tomograms) of a target are collected and mathematically converted to create a virtual Cartesian ultrasound volume. This virtual ultrasound volume facilitates the visualization of non-acquired slices of the target and a variety of rendered surfaces and projections of the target otherwise unobtainable using two-dimensional (2D) ultrasound imaging.
High fidelity 3D ultrasound requires, by definition, a data set in which the spacial relationship between the individual ultrasound slices is precisely known. High fidelity ultrasound is important for the accurate assessment of volumes and the appreciation of target geometry. The conventional method of choice for obtaining the precise spatial relationship between ultrasound slices is to actively constrain the position of each ultrasound slice. This is achieved by controlling the position of the ultrasound probe during generation of the slices by use of a motorized positioning device (mechanical scanning). Examples of 3D ultrasound imaging systems are described in detail in U.S. Pat. Nos. 5,454,371 (Fenster et al.) and 5,562,095 (Downey et al.), the contents of each of which are hereby incorporated by reference.
In the three-dimensional ultrasound imaging systems described in the afore-mentioned United States patents, when a succession of two-dimensional images have been captured and digitized, the two-dimensional images are stored as a stack to form an image data array. Before a three-dimensional image of the scanned volume can be created and viewed by a user, the image data array must be reconstructed to form a volumetric image array. This type of reconstruction, in which every pixel in every two-dimensional image slice is converted into an appropriate voxel in an image volume (i.e. volumetric image array) prior to display is known as “full volume” reconstruction. Full volume reconstruction is shown schematically on the left-hand side of FIG. 1. All the data points (represented by X and O) on each of the individual two-dimensional image slices (collectively A) are generated into a single complete volume array (B). Once the complete volume array has been generated, a selected view of the volume set may be displayed on a monitor (C) by sampling the volume array along selected planes. The generation of the complete volume array is somewhat inefficient, i.e. it is a time-consuming intermediate stage. Full volume reconstruction and display of a three-dimensional image using a conventional hardware platform can take upward of one minute and, therefore, has limited application in situations where immediate display of an acquired image is desirable.
In an attempt to overcome the drawbacks associated with full volume reconstruction, the applicants developed a so-called “fast-linear” reconstruction process which is described in co-pending U.S. patent application Ser. No. 08/562,590 (which corresponds to International patent application serial number PCT/CA96/00777), the contents of which are hereby incorporated by reference.
In fast-linear reconstruction, only the specific image data from the two-dimensional image slices that are actually required to view the user-selected image undergoes reconstruction. In other words, only the image data necessary to view the surface of user-selected image (i.e. as opposed to all of the data representing the entire volume of the target) is used for reconstruction. The fast-linear reconstruction technique is shown schematically on the right-hand side of FIG. 1. If, for example, the users wishes to view a particular image (C) of the target volume, the computer uses associated calibration and aquisition parameters of the collected two-dimensional image slices (A) to determine special “look-up” tables (D) which speed up the determination of which data points from the two-dimensional image slices are required to be displayed on the monitor. In the scenario illustrated in FIG. 1, only the “O” two-dimensional data points necessary to produce the desired image are reconstructed. There is no necessity to construct a full volume image array. Accordingly, this fast-linear reconstruction is more efficient than conventional full volume reconstruction, i.e. it is less time-consuming (less than ½ second).
The fast-linear reconstruction method and system described in co-pending U.S. patent application Ser. No. 08/562,590, can be used to facilitate the display of three-dimensional images of target volumes by the reconstruction of parallel two-dimensional images slices (shown schematically in FIG. 2A) which have been acquired using a linear scanning path. The method and system described may also be utilized when the parallel image slices are uniformly tilted with respect to the scanning axis (shown schematically in FIG. 2B).
It is an object of the present invention to provide a system and method for so-called “fast” reconstruction of fan- and axially-acquired ultrasound data which obviates and mitigates at least one of the disadvantages of the prior art.